Theory maybe they can't find or detect dark matter because we live in a region of the galaxy that has very little of it. It seems to clump and be in regions of space, there is alot of it but maybe not around us or very little. It seems very exotic, doesn't interact with normal matter, strange odd stuff and it's obvious very hard to detect.
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I don't believe that there is any such thing as dark energy or dark matter, and never have done. All that's happened is that scientists have got equations that cannot be balanced unless certain substances exist. So they give those substances names and go looking for them. Never seems to occur to them that the equations might be wrong in the first place. The LHR will keep finding more and more unknown particles that interact in ways we don't yet understand. that is the best way forward, not ghost chasing.

Dark matter was called "missing mass" by Fritz Zwicky in 1935 who analyzed the dynamics of spiral galaxies. Dark energy is called for to explain the acceleration in the expansion of the universe as indicated by studying supernovae as "standard candles" in faraway galaxies. It could have other explanations. The LHC is meant to find the particles predicted by supersymmetry (SUSY) such as neutralinos, which could provide the dark matter, but so far none was found. We shall see what the future holds when it gets to 14 TeV.otherwise we shall have to wait for the next accelerator, the International Linear Collider, to be built in Japan. It's the "Spiral of high energies" foreseen by Angelo Baracca and Silvio Bergia in the Seventies. When an accelerator does not find the particles you are looking for you build a bigger one and cross your fingers.
Tullio
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I too think that there could be other explanations;but. let's wait and see what the best investigators in this field can come up with. Some pooh-poohed the Higgs Boson but it was found as was the Top Quark some time ago.

Once in a while at Test4Theory@home I get a physics lesson from Peter Skands, project chief scientist, when one of the jobs we are running in a window emits some obscure error messages. He then explains to us volunteers the reasons behind them and thanks us for our cooperation.
Tullio
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some invisible material must be providing the gravitational glue to hold galaxies together.

I thought that most scientists think that there is a super massive black hole at the centre of each galaxy that holds all the stars in that galaxy together, by means of gravity. Now what holds the galaxies themsevles in position relative to each other may be a different question. Bits floating on the surface of a bowl of water usually clump together after a certain time but that is due to surface tension.

Sorry, it hasn't. They have found a "Higgs-like particle that needs further investigation.

Should they then give back their Nobel Prizes ??

I say that they have found it- There may be more than one type.

Remember that these are all convenient fictions to explain what we observe. I tell my students that there is no such thing as an electron (as we characterize "it"). We can understand and control electricity effectively however.

Field theory and circuit theory can each be applied successfully to electrical circuits but they are quite different in conceptualization.

some invisible material must be providing the gravitational glue to hold galaxies together.

I thought that most scientists think that there is a super massive black hole at the centre of each galaxy that holds all the stars in that galaxy together, by means of gravity. Now what holds the galaxies themsevles in position relative to each other may be a different question. Bits floating on the surface of a bowl of water usually clump together after a certain time but that is due to surface tension.

Quite happy to be proved wrong!

Close galaxies do merge. I recall reading somewhere that Andromeda is on its way for a collision with Milky Way in a few billion years. I think there are larger structures of galaxies gravitationally bound as well. Galaxies further apart seem to move away due to universal expansion overpowering gravity.
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In the early 1990's, one thing was fairly certain about the expansion of the Universe. It might have enough energy density to stop its expansion and recollapse, it might have so little energy density that it would never stop expanding, but gravity was certain to slow the expansion as time went on. Granted, the slowing had not been observed, but, theoretically, the Universe had to slow. The Universe is full of matter and the attractive force of gravity pulls all matter together. Then came 1998 and the Hubble Space Telescope (HST) observations of very distant supernovae that showed that, a long time ago, the Universe was actually expanding more slowly than it is today. So the expansion of the Universe has not been slowing due to gravity, as everyone thought, it has been accelerating. No one expected this, no one knew how to explain it. But something was causing it.

Dark matter is proof that what we don't know about the universe far exceeds what we do know. And we may never have the capability to comprehend the whole picture. But it doesn't hurt to try.
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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.